<!DOCTYPE html>
<html lang="en">
<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    body {
        height: 100%;
        background: #c6c6c6;
        width: 100%;
        margin: 0;
        padding: 0;
        border: none;
        overflow: hidden;
    }

    canvas {
        margin: 0;
        padding: 0;
        border: none;
    }
</style>
<body>

</body>
</html>
<script type="application/javascript">
    const rate = window.devicePixelRatio
    const canvas = document.createElement('canvas')
    const width = window.innerWidth
    const height = window.innerHeight
    canvas.width = width * rate
    canvas.height = height * rate
    canvas.style.width = width + 'px'
    canvas.style.height = height + 'px'
    document.body.appendChild(canvas)
    window.canvas = canvas
</script>
